cake flour vs. normal flour?

You can use cake flour to subsitute for all purpose flour the breakdown is usually 1cup + 2 tablespoons cake flour for every one cup of all purpose flour. All purpose flour is a bit more dense than cake flour which is why at times you may hear some people suggest sifting your all purpose if you need to substitute it for cake flour. There won't be to much of a difference in taste whereas what your are making may feel a bit lighter in texture when using cake flour as opposed to all purpose.

Yes, you should be fine. Cake flour is low in gluten and with cookies they rise and spread only a little. Cake flour is fine with anything that uses baking powder as the rising agent. Texture will be only slightly different and most people would not notice.

No its not okay! cake flour will change the texture and taste to some extent of the cookies as cake flour usually has rising agent added to it whereas cookie are made with plain flour so that they can retain its shape and texture.

All purpose flour has more gluten in it than cake flour, just use an extra tablespoon per cup of the cake flour.